| 1. |
- Algotsson, Jenny, et al.
(author)
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Electrostatic interactions are important for the distribution of Gd(DTPA)(2-) in articular cartilage.
- 2015
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In: Magnetic Resonance in Medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 76:2, s. 500-509
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Journal article (peer-reviewed)abstract
- The delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) method can be used to assess the content of glycosaminoglycan in cartilage. In in vitro and model studies, the content of glycosaminoglycan is often expressed in terms of a fixed charge density (FCD). Values of the fixed charge density obtained using the dGEMRIC method differs from values obtained using other methods. The purpose of this work was to further clarify the origin of this discrepancy.
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| 2. |
- Algotsson, Jenny, et al.
(author)
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Intermolecular interactions play a role in the distribution and transport of charged contrast agents in a cartilage model
- 2019
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In: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 14:10
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Journal article (peer-reviewed)abstract
- The transport and distribution of charged molecules in polyelectrolyte solutions are of both fundamental and practical importance. A practical example, which is the specific subject addressed in the present paper, is the transport and distribution of charged species into cartilage. The charged species could be a contrast agent or a drug molecule involved in diagnosis or treatment of the widespread degenerative disease osteoarthritis, which leads to degradation of articular cartilage. Associated scientific issues include the rate of transport and the equilibrium concentrations of the charged species in the cartilage and the synovial fluid. To address these questions, we present results from magnetic resonance micro-imaging experiments on a model system of articular cartilage. The experiments yield temporally and spatially resolved data on the transport of a negatively charged contrast agent (charge = -2), used in medical examinations of cartilage, into a polyelectrolyte solution, which is designed to capture the electrostatic interactions in cartilage. Also presented is a theoretical analysis of the transport where the relevant differential equations are solved using finite element techniques as well as treated with approximate analytical expressions. In the analysis, non-ideal effects are included in the treatment of the mobile species in the system. This is made possible by using results from previous Monte Carlo simulations. The results demonstrate the importance of taking non-idealities into account when data from measurements of transport of charged solutes in a system with fixed charges from biological polyelectrolytes are analyzed.
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| 3. |
- Algotsson, Jenny
(author)
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Ions in models of articular cartilage : The importance of electrostatic interactions for transport and equilibrium distribution
- 2017
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Doctoral thesis (other academic/artistic)abstract
- Osteoarthritis (OA) is a degenerative disease that affects articular cartilage, which covers the surfaces of the bones in synovial joints. At later stages the disease can result in major loss of articular cartilage and thus lead to major disability. In order to allow for an early detection and treatment of OA, it is necessary to better understand the rather subtle biochemical changes in the cartilage that occurs at the initial stages of the disease.An important example of a molecular-level change, that is associated with OA is a decrease in the concentration of glycosaminoglycans (GAGs), which are polysaccharides carrying a high density of negative charges. The loss of GAGs can be monitored by, for instance, magnetic resonance imaging (MRI) or computed tomography (CT) in combination with the administration of charged contrast agents. Because of electrostatic interactions between the GAGs, and the charged contrast agent, the concentration of contrast agent in cartilage will depend on the concentration of GAGs and it is found that the partitioning can be described according to the principle of Donnan equilibrium. In the interpretation of MRI data on cartilage, the concentration of contrast agent is commonly related to the concentration of GAGs by the application of ideal Donnan theory, where non-idealities of the involved ions are neglected. Although this assumption is sometimes appropriate, it has been found that analyses of MRI data on cartilage involving ideal Donnan theory in the dGEMRIC method can lead to substantial errors in the estimated GAG concentration. The origin of the discrepancy is debated, but one possibility is that the error arises from the neglect of nonidealities.In the work underlying this thesis, the impact of non-idealities due to electrostatic interactions on the transport and equilibrium distribution of charged species in synovial fluid and articular cartilage has been investigated. To this end, systematic studies were performed on well-defined theoretical and experimental model systems, which were designed to capture the most important ionic features of articular cartilage and the synovial fluid, using a combination of μMRI experiments, Monte Carlo simulations, andfinite element method (FEM) simulations.It was found that the non-idealities arising from electrostatic interactions can, depending on the character of the solute considered, have a substantial influence on the partitioning of a charged solute between cartilage and synovial fluid and, thus, on the applicability of ideal Donnan theory for estimation of the GAG concentration. Importantly, the results from the model systems investigated in this work show good consistency with data on real cartilage found in the literature. Furthermore, non-idealities can also be important to take into account when predicting the rate of transport of a charged solute into cartilage. The results from this thesis are valuable for work towards improving the interpretation of MRI data on cartilage. Since the same mechanisms that control the partitioning of contrast agents are involved in the partitioning of potential drugs, the results are also valuable in the development of drugs to treat OA.
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| 4. |
- Algotsson, Jenny, et al.
(author)
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Monte Carlo simulations of Donnan equilibrium in cartilage
- 2012
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In: Magnetic Resonance in Medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 68:4, s. 1298-1302
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Journal article (peer-reviewed)abstract
- (23) Na magnetic resonance imaging and the delayed gadolinium-enhanced magnetic resonance imaging methods to investigate cartilage can be used to determine the fixed charge density of cartilage. The methods give results that differ by a factor of 2. In this study, we use Monte Carlo simulations on a model system of cartilage and find that the difference originates from the Coulombic intermolecular interactions between the ions in the cartilage, and in the synovial fluid. Those interactions are neglected in the standard Donnan analysis that generally is adopted to evaluate magnetic resonance imaging data. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.
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| 5. |
- Söderman, Olle, et al.
(author)
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Chemical Properties of Cartilage Studied Using Charged Ions
- 2017
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In: Biophysics and Biochemistry of Cartilage by NMR and MRI. - : The Royal Society of Chemistry. - 2044-2548 .- 2044-253X. - 9781782621331 - 9781782629054 ; :8, s. 176-190
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Book chapter (peer-reviewed)abstract
- Articular cartilage is a soft tissue built mainly from collagen and highly negatively charged biological polyelectrolytes. The high negative charge is responsible for crucial properties of cartilage, such as tissue hydration and biomechanical load resistance. As a consequence, breakdown and loss of the polyelectrolytes in cartilage has an adverse effect on its function and there is a need for methods to determine the amount of polyelectrolytes in cartilage. Here we discuss one such method, the delayed gadolinium-enhanced MRI of cartilage (dGEMRIC). dGEMRIC builds on the fact that a negatively charged MRI contrast agent will distribute in an inverse relation to the concentration of polyelectrolytes on account of the electrostatic repulsion between the two. We introduce the method and discuss some of the key assumptions. In particular, we focus on the relaxivity parameter that should be used to convert the measured water spin-lattice relaxation times to a concentration of the contrast agent, the time for reaching equilibrium with respect to penetration of the contrast agent into cartilage and the use of ideal Donnan equilibrium in the further analysis of dGEMRIC data. Finally, we present some examples of clinical applications of the dGEMRIC method.
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| 6. |
- Trulsson, Martin, et al.
(author)
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Differential Capacitance of Room Temperature Ionic Liquids: The Role of Dispersion Forces
- 2010
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In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 1:8, s. 1191-1195
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Journal article (peer-reviewed)abstract
- We investigate theoretical models of room temperature ionic liquids, and find that the experimentally observed camel-shape of the differential capacitance is strongly related to dispersion interactions in these systems. At low surface charge densities, the loss of dispersion interactions in the vicinity of the electrodes generates depleted densities, with a concomitant drop of the differential capacitance. This behavior is not observed in models where dispersion interactions have been removed.
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